For-gnagan

According to the Old English Dictionary:

for-gnagan

p. -gnóg, pl. -gnógon; pp. -gnagen [for-, gnagan to gnaw] To gnaw or eat up; corrōdĕre, comĕdĕre :-- On eallum grówendum þingon hig forgnagaþ omnia quæ nascuntur corrōdent, sive comĕdent, Ex. 10, 5. Gærstapan forgnógon swá hwæt swá se hagol belǽfde locusts gnawed up whatsoever the hail had left, Homl. Th. ii. 194, 1. for-gnagan